Circuit tester for electronic fuzes for munitions



Aug. 16, 1955 F. H. JACKSON CIRCUIT TESTER FOR ELECTRONIC FUZES FOR MUNITIONS Filed July 31, "1946 AUDIO OSCILLATOR VACUUM TUBE VOLT METER INVENTOR FRANK H. JACKSON ATTORNEY CIRCUIT TESTER FOR ELECTRONIC FUZES FOR MUNITIONS Frank E. Jackson, Rochester, N. Y., assignor, by mesue assignments, to the United States of America as represented by the Secretary of the Navy Application July 31, 1946, Serial No. 687,442

7 Claims. (Cl. 3437) The present invention relates generally to testing apparatus for electronic signal devices and more particularly to devices for gauging or measuring a characteristic of electronic fuzes for munitions, commonly known as proximity fuzes.

A radio proximity fuze is a device which detonates an ordnance missile upon attainment of proximity to a target. Such a fuze generally comprises the following essential elements:

1. A radiating system so arranged that its loading is affected by electromagnetic influences incident to target proximity;

2. An oscillator for generating radio-frequency energy and for producing an audio-frequency signal of a substan tial amplitude upon attainment of target proximity; or

la and 2a. An equivalent arrangement for producing such a signal; and

3. An amplifying unit;

4. An electronic discharge device so arranged as to become conductive and fire when target proximity causes the amplified signal applied thereto to become sutficiently great; and

5. A resistance wire or other igniting device energized by the discharge current of the electronic discharge device for causing detonation of the missile.

As the existence of such fuzes has now become generally known, and many circuit and operational features thereof have been published, it is believed to be unnecessary to disclose herein any further details, as such details are not needed in understanding the present invention.

The testing device provided in accordance with the present invention simulates the electrical conditions influencing a proximity fuze as it approaches a target, so that a determination may be made as to whether the fuze will perform properly under actual conditions of operation.

In accordance with the prior art a modulation device was employed for presenting a fixed disturbance or modulating signal of fixed frequency to each one of the proximity fuzes tested during production quality control. The sensitivity of each fuze was determined by measuring with suitable equipment the magnitude of the modulation-signal output of the anode circuit of the oscillator resulting from the application of the fixed modulating signal. However, with the advent of new types of proximity fuzes in which the anode circuit of the oscillator or other signal output terminal is not readily available for measurement, because of the molded construction of the fuze, the only indication which may conveniently be employed in testing is the firing of the thyratron electronic discharge device contained in the fuze. However, the thyratron cannot measure the amount of modulation in the oscillator section. It can indicate only the fact that the output signal from the cascaded oscillator and amplifier sections of such a fuze has attained at least a certain definite magnitude. The testing procedure now becomes one of applying a known modulating signal to the fuze and increasing the signal until the thyratron fires. The magnitude of atent 2,715,725 Patented Aug. 16, 1955 simulated.

Reference is made to the single figure of the drawing, a circuit schematic, partly in block form, of a preferred embodiment of testing device in accordance with the present invention, to the following specification and to the claims appended thereto for a full description of the invention and a showing of other and further objects thereof.

Referring now to the drawing there is illustrated a proximity fuze 10 having an antenna 11 and mounted by suitable means (not shown) within a grounded metallic shield 12. A metallic coupling ring 13 is capacitatively coupled to the antenna 11. The external load imposed on the proximity fuze (impedance from the antenna 11 to ground) also comprises a resistor 14 (20 ohms) and the input impedance of a triode 15. A portion of the high frequency radiant energy transmitted by the proximity fuze passes to the coupling ring 13 and through resistor 14 to ground. The fuze under test is so mounted in the enclosure 12 as to be isolated from the surroundings. By a proper choice of resistance 14 and the position of the coupling ring the percentage of loading on the fuze can be adjusted to approximate that found under standard conditions. This adjustment remains unchanged for any one model of fuze. Resistor 14 is shunted by the input circuit of tube 15, including control electrode or grid 16 and cathode 17. A suitable negative bias is applied to electrode 16 by a battery 18 (1.5 volts) having its positive terminal connected to cathode 17 and its negative terminal connected to resistor 14. The remaining terminal of the last-mentioned resistor is connected to grid 16. The anode 20 is coupled to a suitable source 21 (90 volts) of anode energy through a resistor 22 (10,000 ohms) a radiofrequency choke coil 23 and a secondary winding 24 of a transformer 25. A by-pass capacitor 26 (500 micromicrofarads) connects the junction of elements 22, 23 to ground. The filament 28 of tube 15 is coupled to a suitable source of electricity (not shown) through radiofrequency choke coils 29 and 30 individually included in each lead. By-pass capacitors 31, 32 (each 500 micromicrofarads) connect each side of the filament to ground. Radio-frequency choke coils 29, 30, and 23 and by-pass capacitors 26, 31, and 32 act as simple filters and serve to keep radio-frequency energy from reaching the sources of filament and anode power. The primary winding of transformer 25 is coupled to an audio-frequency signalgenerating oscillator 34. This signal generator is provided with a calibrated output attenuator or an attenuator and measuring device generally indicated as a vacuum tube voltmeter 35. The attenuator and vacuum tube voltmeter combination permits audio-frequency voltages of known magnitude to be applied to the primary winding of transformer 25.

The application of an audio-frequency signal to the primary winding of transformer 25 causes a similar voltage to appear across the secondary winding thereof. This voltage in the transformer secondary winding is effectively in series with the anode voltage and algebraically com-- bines with the latter. Consequently the anodeto-cathode voltage of tube 15 varies at an audio rate whenever an audio-frequency signal is applied to the primary winding of transformer 25. Since the input impedance of a vacuum tube is dependent upon the voltages applied to the various electrodes, application of a varying voltage to the anode of the tube causes a corresponding variation in its input impedance. Since the input impedance of the tube shunts resistor 14, also connected between ring 13 and ground, there is a variation in the impedance from that ring to ground. This variation in impedance appears to the proximity fuze under test as a varying load and the desired modulation of the oscillator anode section thereof results. A standard fuze 10 is first placed in enclosure 12 and the audio-signal amplitude is increased by adjusting the attenuator, mentioned above but not shown, included in the output circuit of audio oscillator 34 until the fuze thyratron fires. The meter 35 is then read and it indicates, by the inverse relationship discussed above, the over-all sensitivity of the fuze. This adjustment and reading are repeated for each fuze. The conformity of the fuzes to the standard is determined by observing whether their discharge tubes fire upon application of an audio signal within predetermined limits.

This testing device has been found satisfactorily to meet the following requirements:

1. The impedance variation caused by the testing device should be such that the modulation voltage appearing in the anode circuit of the oscillator section is sinusoidal in form when the input to the testing device is sinusoidal.

2. There should be a direct linear relationship between the magnitudes of the voltages applied to the testing device and the corresponding modulation voltages appearing in the anode circuit of the oscillator section of the proximity fuze.

3. The first two requirements should obtain for any satisfactory fuze in any range and for modulation voltages of any frequency in the audio range.

4. Adjustment must be provided for obtaining the proper anode ratio or percentage of loading of the fuze being tested (that is, ratio of non-oscillating to oscillating anode current).

While it is not proposed that the invention be limited to any specific circuit dimensions, the parameters hereinabove set forth in parentheses following the components to which they refer are furnished for purposes of illustration, they having been found practicable in one successful embodiment of the present invention. While there has been shown and described what is at present considered to be the preferred embodiment of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the true scope of the invention, and it is, accordingly, intended in the appended claims to cover all such changes as fall within the true scope of the present invention and without that of the prior art.

What is claimed is:

l. A testing arrangement for gauging the sensitivity of a radio signaling device having a radiator, comprising an artificial load coupled to said radiator for imposing radiation resistance thereon, means for electrically isolating the radio signalling device from surrounding objects, means including an interelectrode circuit of a vacuum tube for varying said radiation resistance periodically and continuously within a predetermined range, the relationship between said variation and the response of said device indicating said sensitivity, said artificial load including means surrounding said radio signalling device within said isolation means and coupling said device to said interelectrode circuit.

2. An arrangement in accordance with claim 1 and in which said means for varying said radiation resistance includes the cathode-grid circuit of a vacuum tube, said coupling means comprising a coupling ring.

3. A testing arrangement for gauging a characteristic of a radio signaling device having a signal-amplitude dependent on its load, comprising isolation means for said radio signaling device, an artificial load including a ring mounted in the isolation means and coupling said load to said device, and means for varying a parameter of said load periodically and continuously within predetermined limits, said load including the input impedance of a vacuum tube.

4. A testing arrangement in accordance with claim 3 and in which the last-named means includes a signal generator coupled to the output circuit of said tube and an indicating device for indicating the value of the gauged characteristic.

5. A testing arrangement for gauging a firing characteristic of a proximity fuze, of the type having a radiator, comprising an artificial load for imposing radiation resistance on said radiator, said load comprising a seriesparallel combination of a coupling member, a resistor branch and a variable impedance branch, and calibrated means for varying the impedance of the last-named branch at an audio-frequency rate.

6. A testing arrangement in accordance with claim 5 and in Which the last-mentioned means comprises an oscillator.

7. A testing arrangement in accordance with claim 5, wherein the last mentioned means includes an audio frequency oscillator and a vacuum tube voltmeter.

References Cited in the file of this patent UNITED STATES PATENTS 1,744,036 Brard Jan. 21, 1930 1,793,601 Ferris Feb. 24, 1931 1,793,835 Bruce Feb. 24, 1931 1,911,362 Hickok May 30, 1933 2,047,930 Linder July 14, 1936 2,101,440 Linsell Dec. 7, 1937 2,204,179 George June 11, 1940 2,318,516 Newbold May 4, 1943 2,355,275 Cawein Aug. 8, 1944 2,461,646 Lewis Feb. 15, 1949 2,510,299 Schramm June 6, 1950 

